sendmail: use on-stack buffer for AUTH PLAIN

function                                             old     new   delta
sendmail_main                                       1335    1307     -28

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 27 insertions, 11 deletions

diff --git a/mailutils/sendmail.c b/mailutils/sendmail.c
index 7a4afb835..32c50ba84 100644
--- a/mailutils/sendmail.c
+++ b/mailutils/sendmail.c
@@ -361,19 +361,35 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
                 if (!G.user || !G.pass)
                         get_cred_or_die(4);
                 if (opts & OPT_am_plain) {
-                        char *plain_auth;
-                        size_t user_len, pass_len;
-                        user_len = strlen(G.user);
-                        pass_len = strlen(G.pass);
+                        // C: AUTH PLAIN
+                        // S: 334
+                        // C: base64encoded(auth<NUL>user<NUL>pass)
+                        // S: 235 2.7.0 Authentication successful
+//Note: a shorter format is allowed:
+// C: AUTH PLAIN base64encoded(auth<NUL>user<NUL>pass)
+// S: 235 2.7.0 Authentication successful
                         smtp_check("AUTH PLAIN", 334);
-                        // use \1 as placeholders for \0 (format string is NUL-terminated)
-                        plain_auth = xasprintf("\1%s\1%s", G.user, G.pass);
-                        // substitute placeholders
-                        plain_auth[0] = '\0';
-                        plain_auth[1 + user_len] = '\0';
-                        printbuf_base64(plain_auth, 1 + user_len + 1 + pass_len);
-                        free(plain_auth);
+                        {
+                                unsigned user_len = strlen(G.user);
+                                unsigned pass_len = strlen(G.pass);
+                                unsigned sz = 1 + user_len + 1 + pass_len;
+                                char plain_auth[sz + 1];
+                                // the format is:
+                                // "authorization identity<NUL>username<NUL>password"
+                                // authorization identity is empty.
+                                plain_auth[0] = '\0';
+                                strcpy(stpcpy(plain_auth + 1, G.user) + 1, G.pass);
+                                printbuf_base64(plain_auth, sz);
+                        }
                 } else {
+                        // C: AUTH LOGIN
+                        // S: 334 VXNlcm5hbWU6
+                        //        ^^^^^^^^^^^^ server says "Username:"
+                        // C: base64encoded(user)
+                        // S: 334 UGFzc3dvcmQ6
+                        //        ^^^^^^^^^^^^ server says "Password:"
+                        // C: base64encoded(pass)
+                        // S: 235 2.7.0 Authentication successful
                         smtp_check("AUTH LOGIN", 334);
                         printstr_base64(G.user);
                         smtp_check("", 334);